A typical apparatus for controlling a controlled variable of a rotary machine controls on and off operations of switching elements of a power converter, which are electrically connected to the rotary machine. This controls a value of the controlled variable to follow a command value. An example of such a control apparatus is disclosed in Japanese Patent Application Publication No. 2012-23943, which will be referred to as patent document 1.
The control apparatus disclosed in the patent document 1 uses a phase and amplitude of an output voltage vector of the power converter to control the controlled variable of the rotary machine to match with the command value; the amplitude of the controlled variable will also be called a norm hereinafter. The control apparatus disclosed in the patent document 1 determines a value of the amplitude of the output voltage vector using a map. The map includes a correlation of values of the amplitude of the output voltage vector with respect to values of a rotational speed of a rotor of the rotary machine. Reduction in the accuracy of the correlation of the map may thus result in reduction of the controllability of the rotary machine.
In order to address such controllability reduction, the control apparatus disclosed in the patent document 1 measures an actual value of a d-axis current flowing in the rotary machine and a command value of the d-axis current using a feedback loop. Then, the control apparatus calculates the difference between the actual value and the command value of the d-axis current, and calculates, based on the calculated difference, a correction value for the amplitude of the output voltage vector to thereby reduce the calculated difference. The amplitude correction aims to maintain, at a higher level, the controllability of the controlled variable of the rotary machine even if the accuracy of the correlation of the map decreases.